1. Field of the Invention
The invention relates to a temperature controller of an optical module package, and more particularly, to a temperature controller of an optical module package comprising a first Peltier element for controlling the temperature of an optical element housed in an optical module package, and a second Peltier element for controlling the temperature of the optical module package so as to stabilize the temperature of the optical module package, wherein a second temperature sensing element for detection of the temperature of the optical module package is disposed inside the optical module package in order to control the temperature of the optical module package with the second Peltier element so that precision temperature control and saving of required space can be achieved.
2. Description of the Related Art
With an optical module package incorporating an optical element, control of temperature is generally indispensable to stabilize various characteristics of the optical element. As seen in the case of dual in-line package (DIP), butterfly module package, or the like, stabilization in the temperature of the optical element is normally attempted by incorporating a Peltier element inside the optical module package. However, in case that high precision stability in the temperature thereof is required, stabilization in the temperature of the optical element can be enhanced by the agency of the Peltier element incorporated inside the optical module package in an environment where the temperature of the optical module package in whole has been stabilized by addition of another Peltier element installed at another level.
FIG. 4 is a sectional view showing the schematic construction of a conventional temperature controller of an optical module package, provided with such Peltier elements at two levels. Now the conventional temperature controller of the optical module package is described hereinafter with reference to FIG. 4. Inside an optical module package 1 shown in FIG. 4, a first Peltier element 2 is disposed on and fixed to the bottom surface thereof
A base 3 is disposed on the first Peltier element 2, and an optical element 4 as well as a thermistor 5 acting as a first temperature sensing element are disposed on the base 3. The first Peltier element 2 has a function of controlling the temperature of the optical element 4 while the thermistor 5 has a function of controlling the temperature of the first Peltier element 2 by detecting the temperature of the optical element 4.
Further, the optical module package 1 is disposed over a second Peltier element 6 installed on a base platform 9 or the like with a mount 7 interposed therebetween, and a thermistor 8 acting as a second temperature sensing element is fixedly attached to the mount 7.
The second Peltier element 6 has a function of controlling the temperature of the optical module package 1, and the thermistor 8 has a function of controlling the temperature of the second Peltier element 6 by monitoring the temperature of the mount 7. There are cases where the thermistor 8 is embedded in a recess formed in the mount 7.
With the construction of the temperature controller of the optical module package as described above, control of the first Peltier element 2 is effected by monitoring the temperature of the surface of the base 3 with the thermistor 5 disposed inside the optical module package 1. and the temperature of the optical element 4 is controlled by the first Peltier element 2.
Further, to meet requirement for high precision stability in temperature, stability in the temperature of the optical module package 1 is achieved by installing one additional Peltier element at another level, and controlling the additional Peltier element 6 through monitoring the temperature of the surface of the mount 7 with the thermistor 8 so that stability in the temperature of the optical element 4 is attained by the agency of the first Peltier element 2 housed in the optical module package 1 in an environment where the temperature of the optical module package 1 in whole is stabilized.
As shown in FIG. 4, with the conventional temperature controller, stabilization in the temperature of the optical element 4 inside the optical module package 1 has been attempted for by installing Peltier elements at two or more levels. However, with the construction shown in FIG. 4, the thermistor 8 is installed on the mount 7 disposed on the second Peltier element 6, exposing the thermistor 8 and the mount 7 directly to open air. Consequently, the thermistor 8 and the mount 7 are subjected to the effect of open air temperature, creating a cause for erroneous monitoring. This has made it impossible to monitor accurate temperatures, resulting in unstable control of the temperature of the second Peltier element 6 and consequently, that of the optical element 4. Thus a problem of deviation from target temperatures for control has been encountered.
There has been a known countermeasure of shielding the optical module package from open air by covering the external surface thereof with a heat insulating material such as cork or the like, however, in this case, another problem has arisen that an extra space more than necessary is required.